Is it possible?

im absolutely positive the only day i had unprotected sex was Jan 13th and was supposed to get my period around the 20th , missed & took it pregnancy test the 25th and got a BFP .... isn't that to quick to show up ? or could it have been another time and maybe the condom ripped ? im confused because the 13th was the only time I've ever had sex unprotected to my knowledge ...